Information storage drive systems often operate by holding an electromagnetic transducer or head next to a relatively moving magnetic media, such as a disk or tape. The media typically moves in a single direction, so that a stationary transducer can read or write bits of data on a single track that passes next to the transducer, while the employment of a transducer that can move in a direction transverse to the media motion allows access to multiple tracks. Such moveable transducers are commonly attached near distal ends of suspensions in order to facilitate access to various tracks. It is important that a suspension accurately position the transducer along as well as across a recording track in order to eliminate errors and reduce noise.
In order to provide such accurate positioning, a suspension load beam is typically stiff in both lengthwise ("longitudinal") and sideways ("lateral") directions, which are both oriented substantially parallel to the plane of the media. Lateral and longitudinal stiffness affords rapid access of a head to various tracks of the media, reduces settling time and increases the ability of the head to follow a single track, all essential to increased drive performance. Stiffness in a given direction of a beam generally correlates with high resonant vibration frequencies of the beam in vibration modes corresponding to those directions, so a greater stiffness or flexibility can be translated into, respectively, a higher or lower resonant vibration frequency. In other words, high resonant vibration frequencies generally reduce positioning error, as perturbations such as may be induced by transducer movement between tracks do not result in large position errors and are quickly diminished, allowing the transducer to accurately read or write.
On the other hand, flexibility of a beam in a direction toward and away from the media, which is termed the "vertical" or "perpendicular" direction in the present invention, is generally desirable to allow the transducer to conform to variations in media height or positioning and to provide a spring force for holding the transducer next to the media, which may include controlling fly height. This bending is typically achieved by creating a spring or hinge portion near a base or mounting end of the beam. Flexibility in the vertical direction, however, may allow undesirable low-frequency resonant vibrations to occur in a torsional mode, since torsional vibration can occur when laterally spaced portions of the beam bend in opposite vertical directions. A torque on the beam is generally induced with any lateral acceleration, which occurs for instance when the head shifts between tracks, since the center of mass of the head is not aligned with the torsional axis of the beam or gimbal. There is a fundamental conflict between the need to allow vertical bending of the beam and the need to reduce the amplitude of torsional vibrations, since the torsional vibrations are simply vertical bending in which one side of the beam is out of phase with the other. These torsional vibrations can cause significant off-track motion leading to noise and errors in reading and/or writing data, and impeding any reduction in transducer access time between tracks.
An object of the present invention is to provide means for preferentially increasing torsional stiffness of a transducer suspension without reducing the vertical bending flexibility.